5 expanded posts ยท every known parent and child
To: cypherpunks@toad.com C.>No doubt this will eventually be marketed as a feature you can pay C.>extra for... intended so people can track their spouses' movements C.>so they know when they're getting home, if they're stuck in a traffic C.>jam, etc. Bell Atlantic already announced a joint venture with one of the electronic navigation companies to supply drivers with position info using cellular triangulation. DCF --- WinQwk 2.0b#1165
>Bell Atlantic already announced a joint venture with one of the electronic >navigation companies to supply drivers with position info using cellular >triangulation. Not to mention our very own Omnitracs service, which uses spread spectrum ranging via satellite to report the position of every mobile user to roughly GPS accuracy (without actually using GPS). So far the trucking companies to whom we sell this stuff have been pretty enlightened in how they use this information. We've also discussed adding position location to our CDMA cellular system, although that wasn't originally a design consideration. Depending on how far you go with modifying the existing system, and depending on local terrain, you could locate a user somewhere on a circle around a given cell (by round trip time measurements from cell to mobile and back) or perhaps to a specific point by multi-cell delay measurements during a handoff. Which suggests a "stealth" phone that randomly dithers its round trip delay a la GPS selective availability... Phil
Which suggests a "stealth" phone that randomly dithers its round trip delay a la GPS selective availability... Well, I'm not sure how well that would work... The "dither" on the RTT can't go negative (for obvious reasons :-) ). Presumably the dither turns a "He's somewhere on this circle" into a "He's somewhere inside this circle". If you vary the dither over time, someone trying to track you would wait for the RTT to hit a local minimum to get the most precise fix. If the dither introduced by the phone has to be the same for all cell sites, it gets even easier. - Bill
>Well, I'm not sure how well that would work... The "dither" on the >RTT can't go negative (for obvious reasons :-) ). Sure it can. We're not talking RTT in the Internet sense. In a spread spectrum system, deterministic pseudo-random sequences are used for the spreading codes; the receiver always knows the future of the sequence. We generate ours with conventional linear feedback shift registers. The mobile phone tracks the code phase of the cell site and slaves its own coded transmissions to that. All you'd have to do is to add a random time-varying phase to the tracking loop. That would cause the measured delay to be either greater than or less than the real value. There would be limits to how far you could vary the delay, but the tolerance at the cell has to be on the order of the cell radius for the system to work anyway. Phil
C'punks, On Wed, 22 Jun 1994, Bill Sommerfeld wrote: > Which suggests a "stealth" phone that randomly dithers its round trip > delay a la GPS selective availability... > > Well, I'm not sure how well that would work... The "dither" on the > RTT can't go negative (for obvious reasons :-) ). > . . . Why not? Of course it would reveal the dithering, but your location would still be ambiguous. One would assume if someone were on the run, there would be only minimal advantage in have a legitimate looking ping location. The major emphasis would be in not getting caught. S a n d y